Image data rotation apparatus

ABSTRACT

An image processing apparatus includes: a first memory for storing 2-D image data wherein pixels are arranged in a matrix in the main scanning direction and sub-scanning direction orthogonal to each other; a second memory; and a data control section for controlling the first memory and second memory, wherein at least one of the first and second memories is constituted by a SDRAM. The data control section reads the image data from the first memory in blocks of m pixels in the main scanning direction and n pixels in the sub-scanning direction (where n and m are natural numbers), writes the read data into the second memory, and transmits data to the memory composed of the SDRAM by burst transmission and continuous supply of desired column addresses, thereby allowing the read image data to be rotated.

BACKGROUND OF THE INVENTION

The present invention relates to an image data rotation apparatus forrotating image data.

A copying machine or similar apparatus uses the rotation method, whereinwhen rotating one-page image data, the entire page is rotated by therepeating the steps of scanning the image data in blocks each consistingof m pixels by n pixels (where m and n denote natural numbers) from theimage memory; applying a 90-degree or 180-degree rotation to each block;and writing the block having been rotated, into a predetermined locationof the page memory.

As shown in FIG. 7, for example, when the image data of one blockconsisting of four pixels by n pixels is scanned from an image memory102, the four-pixel image data items D1 through D4 continuously arrangedon one and the same line are read as the one-row image data of theblock. Reading of each row is repeated n times, whereby one-block imagedata is read.

An image data rotation apparatus is disclosed (for example, JapanesePatent Tokkai 2000-268169) wherein the burst mode of SDRAM (SynchronousDynamic Random Access Memory) is employed to increase the processingspeed in the reading and writing of image data in blocks, as describedabove.

In the SDRAM burst mode, as shown in FIGS. 8( a) through 8(d), when thecolumn address (COL) has been given after the row address (ROW), theSDRAM automatically increments the column address until the presetnumber of bursts (4 in this case) has been reached, thereby reading thedata continuously.

In this apparatus, the one-row image data items D1 through D4 of theblock are stored in the continuous addresses on the image memory 102.This is utilized to read and write the one-row image data in the SDRAMburst mode, thereby increasing data transfer speed.

In the SDRAM burst mode, the address is automatically incremented “1” bythe number of bursts from the column address given in the beginning.Thus, this applies only to the cases where the image data itemsconstituting one row of the block are arranged in the continuousaddresses on the image memory. Consequently, this prior art is incapableof simultaneous processing of rotation and reduction by reading theone-row image data on the block while thinning out pixels.

SUMMARY OF THE INVENTION

The present invention has been made to solve the aforementioned problem.It is the object of the present invention to provide an image datarotation apparatus capable of enlargement and reduction of an imagesimultaneously with the rotation thereof, while maintaining thehigh-speed access to the image memory.

The aforementioned object can be achieved by any one of the structures(1) through (5) described below:

(1) An image processing apparatus comprising: a first memory for storing2-D image data wherein pixels are arranged in a matrix in the mainscanning direction and sub-scanning direction orthogonal to each other;a second memory; and a data control section for controlling theaforementioned first memory and second memory, wherein at least one ofthe first and second memories is constituted by an SDRAM; and the datacontrol section reads the image data from the first memory in blocks ofm pixels in the main scanning direction and n pixels in the sub-scanningdirection (where n and m are natural numbers), writes the read data intothe second memory, and performs the processing of data transmission tothe memory composed of the aforementioned SDRAM by burst transmissionand continuous supply of desired column addresses, thereby allowing theread image data to be rotated.

(2) The image processing apparatus described in the structure (1)wherein the aforementioned data control section gives one of the rowaddresses inside the SDRAM to enable transmission of the image data inthe row, and sequentially selects a desired column in the row address,thereby allowing the image data of the selected column to betransmitted.

(3) The image processing apparatus described in the structure (1)wherein the aforementioned data control section, when selecting adesired column address in the row address, thins out the columns, andtransmits the data.

(4) The image processing apparatus described in the structure (1)wherein each of the first and second memories is constituted by anSDRAM.

(5) The image processing apparatus described in the structure (1)wherein the first and second memories are arranged in one and the sameSDRAM.

The aforementioned object can also be achieved by any one of morepreferable structures (6) through (10).

(6) An image data rotation apparatus, comprising the steps of: readingthe image data in blocks each having m pixels in the main scanningdirection by n pixels in the sub-scanning direction (where m and ndenote natural numbers), from the image memory storing the 2-D imagedata arranged in a matrix in the main scanning direction andsub-scanning direction orthogonal to each other; applying rotation tothis image data; and writing the image data having been rotated into theimage memory, wherein at least either the image memory from which theimage data is read or the image memory to which it is written iscomposed of an SDRAM, and access to this SDRAM is made in the burstaccess mode according to the random column method.

According to the structure (6), when the image data in blocks eachconsisting of m pixels by n pixels is read from or written into theimage memory composed of the SDRAM, access to this SDRAM is made in theburst access mode by the random column method. The random column methodis a mode of operation wherein desired column addresses are given on acontinuous basis when the SDRAM is activated by a row address assignedthereto, and access is made to the areas specified by this row addressand column address one after another, thereby allowing the process ofreading and writing to be performed.

The burst access according to the random column method allows access todesired addresses on a continuous basis if the area belongs to one rowaddress. This ensures high-speed data transmission and flexible addressconfiguration. Since the random column method cannot use the automaticincrement function of the address of the SDRAM, the column addressassigned to the SDRAM is generated by the image data rotation apparatus.

It does not matter from which part in one block the image data is reador written in one process of burst access according to the random columnmethod. For example, the image data of one row of the block or the imagedata of the entire block may be read and written in one burst accessoperation if the image of n-line in the main scanning direction isstored in one row address.

(7) The image data rotation apparatus described in the structure (6)wherein the image data of a plurality of pixels arranged in the mainscanning direction is read or written in the burst access mode accordingto the random column method.

According to the structure (7), the image data of a plurality of pixelsarranged in the main scanning direction is read or written in the burstaccess mode according to the random column method. For example, if theimage data of one row (m pixel) in the main scanning direction is readand written in one operation of burst access, then the image data of oneblock can be read and written in n-operations of burst access.

(8) The image data rotation apparatus described in the structure (6) or(7) wherein the image memory from which the data is read is composed ofa plurality of work memories having the area for all the pixels on oneline in the main scanning direction, by n pixels, and the work memoriesare switched sequentially to form an image memory from which the data isread.

According to the structure (8), a plurality of work memories arrangedfor the n-line are switched for use as the image memory from which thedata is read. For example, while the image data rotation apparatus isperforming the process of reading the one-line image data stored in awork memory in units of blocks, the next n-line image data is stored inanother work memory. A minimum of two work memories is required.

(9) The image data rotation apparatus described in the structure (8)wherein the image memory in which the image data having been rotated iswritten is a page memory, and the aforementioned work memory is arrangedin the unoccupied area of the SDRAM constituting the page memory.

According to the structure (9), the work memories are provided in theunoccupied area of the SDRAM constituting the page memory. Since thestorage capacity of the SDRAM can be increased or decreased only in acertain unit (unit conforming to the number of bits in the address),normally the memory capacity required for the page memory and the SDRAMstorage capacity do not agree with each other, and some fragmentary arearemains. This remaining area is used to arrange the work memory.

(10) The image data rotation apparatus described in the structure (6),(7), (8) or (9) wherein an image is enlarged or reduced by controllingthe address when making burst access according to the random columnmethod.

According to the structure (10), when the image data is read or writtenin blocks among the image memories, an image is enlarged or reduced bycontrolling the address when making burst access according to the randomcolumn method. To be more specific, when the m pixels are read in themain scanning direction by burst access in the random column method, ifthe column addresses provided by the SDRAM are generated in adiscontinuous manner, and the pixels are thinned out; then the imagedata can be read by the image data rotation apparatus while beingreduced in the main scanning direction. If the same column address isgenerated several times, the image data can be read and written whilebeing enlarged in the main scanning direction.

According to the image data rotation apparatus of the present invention,when image data is written in the image memory composed of the SDRAM inblocks each consisting of m pixels by n pixels, access to the SDRAM ismade in the burst access mode of the random column method. Thisarrangement provides flexible addressing for data transmission betweenthe image memory and image data rotation apparatus.

If the column addresses assigned to the SDRAM are discontinuouslygenerated or the same address is generated several times, theenlargement or reduction of the image can be performed simultaneouslywith image rotation, while the high speed of access due to burst accessmode is maintained. Thus, this arrangement has the advantage ofimproving the overall processing speed as compared to the case whererotation is performed separately from enlargement/reduction.

In a system provided with a plurality of work memories consisting of allthe pixels on one line in the main scanning direction, by n pixels,where these work memories are switched for use as the image memory fromwhich the data is read, the storage capacity required for the imagememory will be reduced. Further, if the area of SDRAM remaining afterhaving been reserved for the page memory is used to arrange the workmemories, the required number of the memory devices will be reduced,with the result that the price of the apparatus can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representing the configuration of a digitalcopying machine including an image data rotation apparatus as anembodiment of the present invention;

FIG. 2 is an explanatory diagram of the data flow showing the process ofrotating the image data sequentially inputted from an image readingsection, and loading them into the page memory;

FIG. 3 is an explanatory diagram representing how the data controlsection rotates the image in blocks at a scaling factor of 100%.

FIGS. 4( a) through 4(d) are the timing charts showing various signalsin the case of burst access by incrementing the column addresses by “1”in the random column method;

FIGS. 5( a) through 5(d) are the timing charts showing various signalssent to the memory section by the data control section during imagerotation, with the length in the main scanning direction being reducedto a half;

FIG. 6 is an explanatory diagram showing that image data is read intothe rotation register from the work memories by skipping every otherpixel;

FIG. 7 is an explanatory diagram showing that the image data is read in4-pixel by n-pixel blocks from the image memory in the prior art imagedata rotation apparatus; and

FIGS. 8( a) through 8(d) are the timing charts representing the statesof various signals when the burst mode of the SDRAM is used toautomatically increment the column address.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following describes the preferred embodiment of the presentinvention with reference to drawings:

FIG. 1 shows the configuration of a digital copying machine 10 includingan image data rotation apparatus as an embodiment of the presentinvention. The digital copying machine 10 has an image reading section11, a data control section 20, an image printing section 12 and a memorysection 30.

The image reading section 11 has a function of reading a 2-D image byrepeatedly reading the image of one line in the main scanning directionwhile shifting the reading position in the sub-scanning directionorthogonal to the main scanning direction. Here it has a light sourceextending in the main scanning direction for applying light to adocument, a line image sensor for reading one line of the document inthe main scanning direction, a shifting device for shifting the readingposition in units of line in the sub-scanning direction, and an opticalpath consisting of a lens and mirror for leading the reflected lightfrom the document, to the image sensor and forming an image. The lineimage sensor contains a CCD (charge coupled device). The analog imagesignal outputted from the line image sensor is subjected toanalog-to-digital conversion, and is read as digital image data.

The image printing section 12 allows the image corresponding to theimage data to be formed on a recording medium by the electrophotographicprocess, and to be outputted. The image printing section 12 isconfigured as a so-called laser printer that has a recording paperconveyance apparatus, a photoconductor drum, a charging device, a laserunit, a development apparatus, a transfer and separation apparatus, acleaning apparatus and a fixing apparatus.

The memory section 30 is a memory for storing the image data, and iscomposed of an SDRAM. The memory section 30 has a page memory 31 of thesize capable of storing the document of the maximum size that can beread by the image reading section 11, at the maximum resolution. Thefirst work memory 32 and second work memory 33 are provided in the arearemaining after the page memory 31 has been reserved. In thisembodiment, the first and second work memories 32,33 are provided as afirst memory, and the page memory 31 is provided as a second memory.Further the first and second memories are composed of SDRAM both.

The first work memory 32 and second work memory 33 each have the sizecovering all the pixels on one line in the main scanning direction, byn-lines, when the document of the maximum size that can be read by theimage reading section 11 has been read at the maximum resolution. Hereeach pixel is represented in 8-bit multiple gradations, and one pixel iscarried by one byte. Further, the memory section 30 has an 8-bit databus width. Thus, the memory section 30 has image data of one pixelstored in one address.

The data control section 20 as an image data rotation apparatus performsa function of controlling the flow of image data. To be more specific,it performs a function of storing the image data read by the imagereading section 11, in the work memories 32 and 33 of the memory section30; a function of reading the image data from the work memories 32 and33 in blocks each consisting of m pixels in the main scanning direction,by n-lines in the sub-scanning direction, and rotating it; a function ofwriting the image data having been rotated, into the page memory 31; anda function of outputting the image data to the image printing section 12from the page memory 31. In this case, m=n=4.

To perform the aforementioned functions, the data control section 20 isprovided with a setting register 21, a sequence control section 22, anaddress generation section 23, an image rotation processing section 24and a rotation register 25.

The setting register 21 stores the information of various typesrepresenting the operation conditions as well as operation instructions.For example, the number of the pixels, in the main scanning direction,of the document read by the image reading section 11, the number oflines in the sub-scanning direction, the leading addresses of the pagememory 31, first work memory 32 and second work memory 33, the angle ofrotation, scaling factor in the main scanning direction, and startupcommand are inputted, set and registered. They are inputted from the CPU(Central Processor Unit) (not illustrated) that administers theoperations of the digital multifunction device 10.

The sequence control section 22 controls the flow of a sequence ofprocesses performed by the data control section 20. The addressgeneration section 23 generates the address signals and command signalsto access the page memory 31, first work memory 32 and second workmemory 33. The rotation register 25 registers the one-block image dataread from the work memories 32 and 33, in the register.

The image rotation processing section 24 stores the image memory intothe rotation register 25 and reads the image data from the rotationregister 25. The image is rotated by controlling the direction ofstoring into the rotation register 25 and direction of reading from therotation register 25. The angle of rotation is any one of 0, 90, 180 and270 degrees.

FIG. 2 is a data flow showing the process of rotating the image datasequentially inputted from the image reading section 11, and loadingthem into the page memory 31. When the image reading section 11 hasstarted to read the document, the image data is sequentially inputtedfrom the image reading section 11 to the data control section 20 (P1).To be more specific, the image data on one line in the main scanningdirection is sequentially inputted from the top position of the page tothe end position.

The data control section 20 switches between the first work memory 32and second work memory 33 alternately so that one of them is used as awork memory to store the image data to be inputted sequentially from theimage reading section 11, and the other is used as a work memory fromwhich the image data for rotation is read. To be more specific, when theimage data inputted from the image reading section 11 is stored in thefirst work memory 32 (P2 a), the image data for rotation is read fromthe second work memory 33 in blocks (P3 a). In the meantime, when theimage data inputted from the image reading section 11 is stored into thesecond work memory 33 (P2 b), the image data for rotation is read inblocks from the first work memory 32 (P3 b).

The image data read into the rotation register 25 of the data controlsection 20 is rotated and is then stored in the page memory 31 (P4).When the image reading section 11 stores the four-line data into one ofother work memories, the four-line data stored in the other work memoryhas already been rotated, and is stored in the page memory 31.

As described above, the image reading by the image reading section 11and rotation are performed simultaneously in a flow working system inparallel with each other, and the first work memory 32 and second workmemory 33 are alternately switched so that they will alternately operateas the memory to which the data is stored and the memory from which thedata is read. This arrangement reduces the storage capacity required asthe image memory from which data is read, with the result that workmemories 32 and 33 can be located in the area remaining after the pagememory 31 has been reserved from the memory section 30.

FIG. 3 is an explanatory drawing representing how the data controlsection 20 rotates the image in blocks at a scaling factor of 100%. InFIG. 3, first work memory 32 is used as the memory from which data isread, and rotation is applied to the leading block in the main scanningdirection.

The data control section 20 ensures that the image data items a1, a2, a3and a4 of four pixels continuously arranged from the top of the firstline is read in the burst access mode according to the random columnmethod. In this example, rotation is applied at a scaling factor of100%; therefore, the column addresses are generated in such a way thatthey are incremented by “1”.

FIGS. 4( a) through 4(d) show the statuses of various signals given tothe memory section 30 by the data control section 20 when the image dataitems a1, a2, a3 and a4 are read in the burst access mode according tothe random column method. The address information is given to the SDRAM,with the high-order row address being separated from low-order columnaddress. The activation command “ACT” and the row address correspondingto the leading address of the first line are given first. This activatesthe-storage area belonging to one and the same row address, and enablesdata read/write operations.

After that, the “READ” command for designating the reading of data andthe first column address “COL” are given. Then the column addresses“COL+1”, “COL+2” and “COL+3” each incremented by one are givencontinuously. This operation allows the image data items a1, a2, a3 anda4 to be read continuously.

As shown in FIG. 3, the four-pixel image data items a1, a2, a3 and a4are sequentially loaded in the first row of the rotation register 25forming a 4×4 matrix. In the similar manner, the four-pixel image dataitems b1, b2, b3 and b4 from the top of the second row of the first workmemory 32 increment the column addresses by “1” in the burst access modeaccording to the random column method, and are read out continuously andstored in the second row of the rotation register 25.

In the similar manner, the four-pixel image data items c1, c2, c3 and c4from the top of the third row of the first work memory 32 and thefour-pixel image data items d1, d2, d3 and d4 from the top of the fourthrow of the first work memory 32 are read in the third and fourth rows ofthe rotation register 25.

When the image is rotated 90 degrees to the left, the pixel a1 on thefirst row and first column of the rotation register 25, the pixel b1 onthe second-row and first column, the pixel c1 on the third row and firstcolumn, and the pixel d1 on the fourth row and first column are writtenin the four-pixel position from the top of the line at the end of thepage of the page memory 31 in the main scanning direction. In this caseas well, the column addresses are incremented by “1” in the burst accessmode according to the random column method, and four pixels are writtencontinuously.

The pixel a2 in the first row and second column of the rotation register25, the pixel b2 in the second row and second column, the pixel c2 inthe third row and second column and the pixel d2 in the fourth row andsecond column are written in four-pixel positions from the top in themain scanning direction on the second line from the end of the page ofthe page memory 31. In this case as well, the column addresses areincremented by “1” in the burst access mode according to the randomcolumn method, and four pixels are written continuously.

In the similar manner, the pixel a3 in the first row and third column,the pixel b3 in the second row and third column, the pixel c3 in thethird row and third column and the pixel d3 in the fourth row and thirdcolumn are written in four-pixel positions from the top in the mainscanning direction on the third line from the end of the page of thepage memory 31. The pixel a4 in the first row and fourth column, thepixel b4 in the second row and fourth column, the pixel c4 in the thirdrow and fourth column and the pixel d4 in the fourth row and fourthcolumn are written in four-pixel positions from the top in the mainscanning direction on the fourth line from the end of the page of thepage memory 31.

FIGS. 5( a) through 5(d) show examples of the states of various signalssent to the memory section 30 by the data control section 20 duringimage rotation, with the length in the main scanning direction beingreduced to a half. When the image data of four pixels in the mainscanning direction is read into the first row of the rotation register25 from the work memories 32 and 33, the address generation section 23generates the column addresses by incrementing by “2”.

To put it another way, after the first column address “COL” has beengiven, the column addresses each incremented by “2”—“COL+2”, “COL+4” and“COL+6”—are supplied continuously. This arrangement allows the imagedata items a1, a3, a5 and a7 to be read continuously.

As the image data is read as described above, as shown in FIG. 6, theimage data is read from the work memory by skipping every other pixel.The image data items a1, a3, a5 and a7 are read in the first row of therotation register 25 forming a 4-pixel by 4-pixel matrix, and 50%thinning out is carried out in the main scanning direction in the readoperation for rotation.

In the random column method, the method of generating the address ischanged in response to the preset scaling factor. For example, when theimage is enlarged to 200% and is read from the work memory, while thesame column address is generated twice, the address should beincremented.

In the enlargement/reduction mode, it is also possible to make sucharrangements that processing of error diffusion is applied: based onthis result, the column address is produced by the data control section,and data is transferred.

Processing of enlargement/reduction in the sub-scanning direction can beperformed simultaneously by designating the row address as appropriate.For example, a reduction to 50% in size can be achieved by designatingevery other row, and an enlargement to 200% can be provided bydesignating the same row twice. In this manner, processing of rotationand scaling (enlargement/reduction) can be performed in the main andsub-scanning directions simultaneously.

The processing of enlargement/reduction in the sub-scanning directioncan be performed separately.

Further, processing of enlargement/reduction in the sub-scanningdirection is performed separately. For example, in the case of reductionto 50%, the image data from the work memory should be read by skippingevery other line, and in the case of enlargement to 200%, the same lineshould be read twice; alternatively, the same line should be writtentwice at the time of writing into the page memory 31.

As described above, if access to the page memory 31 formed by the SDRAMand work memories 32 and 33 is made in the burst access mode accordingto the random column method, then flexible selection of the image datato be read, as well as high-speed data read/write operation, can beensured.

Although the embodiments of the present invention have been describedwith reference to drawings, it should be clearly understood that aspecific configuration is not restricted to the illustrated embodiments.The present invention can be embodied in a great number of variationswith appropriate modification or additions, without departing from thetechnological spirit and scope of the invention claimed. For example, itis also possible to make such arrangements that generation of theaddress in the random column method is restricted to the case whereimage data is read from the work memories 32 and 33, and writing intothe page memory 31 is carried out in the normal burst mode where theaddresses are automatically incremented.

In the aforementioned description of the embodiment, two work memoriesare alternately switched for use. However, it is also possible toarrange such a configuration that three or more work memories areprovided so that they can be switched in a designated order. In thiscase, a certain allowance will occur in the relationship betweenrotation speed and reading speed of the image reading section 11.Further, the image memory from which image data is read can be a pagememory.

In addition, in the aforementioned description of the embodiment,reduction or enlargement in the main scanning direction is carried outby controlling the column address. However, the flexibility of thecolumn address can be used otherwise. For example, the direction ofreading the image data from the work memories can be reverse to the mainscanning direction (column address decremented), whereby the image ischanged into a mirror image. Further, formation of a mirror image andreduction can be performed simultaneously.

When the image data of a plurality of lines can be stored in the areaactivated by one row address, it is also possible to arrange such aconfiguration that the image data of a plurality of rows of the block isobtained in one burst access operation.

In the aforementioned description of the embodiment, access is made in4-pixel by 4-pixel blocks. Desired numbers of pixels in the main andsub-scanning directions can be selected. They can be selected inconformity to the number of lines of the work memory that can bereserved in the memory section 30 and the matrix size of the rotationregister 25 that can be accommodated in the data control section 20, forexample.

Further, in the aforementioned description of the embodiment, columnaddresses are sequentially using a constant on a regular basis. Withoutbeing restricted thereto, the random column method allows the columnaddresses to be designated irregularly.

1. An image data rotation apparatus comprising: (a) a first memory forstoring 2-D image data wherein pixels are arranged in a matrix in a mainscanning direction and sub-scanning direction orthogonal to each other;(b) a second memory; and (c) a data control section for controlling thefirst memory and the second memory, wherein at least one of the firstand second memories is constituted by a SDRAM, and the data controlsection reads the image data from the first memory in blocks of m pixelsin the main scanning direction and n pixels in the sub-scanningdirection, writes the read data into the second memory, and transmitsdata to the memory composed of the SDRAM by conducting bursttransmission and continuous supply of desired column addresses, therebyallowing the read image data to be rotated, where n and m representnatural numbers, wherein the data control section gives one of rowaddresses inside the SDRAM to enable transmission of image data in therow, and sequentially selects a desired column in the row addresses,thereby allowing the image data of the selected column to betransmitted, and wherein when selecting the desired column address inthe row address, the data control section thins out the columns, andtransmits the data.
 2. The image data rotation apparatus of claim 1,wherein each of the first and second memories is constituted by anSDRAM.
 3. The image data rotation apparatus of claim 1, wherein thefirst and second memories are arranged in the same SDRAM.
 4. An imagedata rotation apparatus, comprising: (a) a first memory for storing 2-Dimage data arranged in a matrix in a main scanning direction andsub-scanning direction orthogonal to each other; and (b) a second imagememory for storing image data output form the first image data, whereinimage data in blocks having m pixels in the main scanning direction by npixels in the sub-scanning direction where m and n denote naturalnumbers, is read from the first image memory, the read image data arerotated, and the rotated image data are written into the second imagememory, and wherein at least one of the first and second image memoriesis constituted by a SDRAM, and access to the SDRAM is made in a burstaccess mode according to a random column method, and wherein the imagedata of a plurality of pixels arranged in the main scanning directionare read or written in the burst access mode according to the randomcolumn method.
 5. The image data rotation apparatus of claim 4, whereinthe first image memory from which the data are read is composed of aplurality of work memories having the area for all the pixels on oneline in the main scanning direction, by n pixels, and the work memoriesare switched sequentially to form an image memory from which the dataare read.
 6. The image data rotation apparatus of claim 5, wherein thesecond image memory in which the image data having been rotated arewritten is a page memory, and the work memory is arranged in anunoccupied area of the SDRAM constituting the page memory.
 7. The imagedata rotation apparatus of claim 4, wherein an image is enlarged orreduced by controlling an address when conducting burst access accordingto the random column method.
 8. An image data rotation apparatus,comprising: (a) a first memory for storing 2-D image data arranged in amatrix in a main scanning direction and sub-scanning directionorthogonal to each other; and (b) a second image memory for storingimage data output form the first image data, wherein image data inblocks having m pixels in the main scanning direction by n pixels in thesub-scanning direction where m and n denote natural numbers, is readfrom the first image memory, the read image data are rotated, and therotated image data are written into the second image memory, and whereinat least one of the first and second image memories is constituted by aSDRAM, and access to the SDRAM is made in a burst access mode accordingto a random column method, wherein the first image memory from which thedata are read is composed of a plurality of work memories having thearea for all the pixels on one line in the main scanning direction, by npixels, and the work memories are switched sequentially to form an imagememory from which the data are read.